Combinatorial chemistry refers to techniques to fabricate, test, and store the resulting data for a material library containing tens, hundreds or even thousands different materials or compounds. Combinatorial investigations require rapid screening techniques to test and evaluate variations of composition, structure and property within a material library. X-ray diffraction is one of the most suitable screening techniques because abundant information can be revealed from the diffraction pattern and X-ray diffraction is fast and non-destructive.
An x-ray diffraction system for use in combinatorial chemistry was reported on in a recent journal (Bob. B. He, John Anzelmo, Peter LaPuma, Uwe Preckwinkel and Kingsley. L. Smith, “XRD Rapid Screening System for Combinatorial Chemistry”, Advances in X-ray Analysis, Vol. 44, the 49th Annual Denver X-ray Conference, Denver, Colo., USA, 2000). All of the components of the system are mounted on a vertical goniometer, and the samples are located a multiple-cell sample tray mounted on a sample support that is movable in three dimensions. An x-ray source and an x-ray detector are each located at an angle relative to the top surface of the sample tray such that x-ray energy from a sample under test is diffracted toward the detector. A laser video system is used for automatic alignment of the sample under test, and allows each sample cell to be sequentially and automatically placed at the testing location.
Although the aforementioned system provides a means for combinatorial screening using automated x-ray diffraction analysis, it is limited to “reflection mode” analysis. That is, the x-ray source and the detector are located to the same side of the sample holder. In certain circumstances, however, it is desirable to perform a sample analysis using “transmission mode” analysis due to various reasons, including the need for low angle diffraction, and advantages when testing thin samples or samples in liquid environments.